The parasympathetic cardiac ganglion of Necturus maculosus (mudpuppy) will be used to investigate the histochemical organization and synaptic integration occurring in a vertebrate cardiac ganglion. The mudpuppy cardiac ganglion contains two neuron types: postganglionic cells and intrinsic SIF cells. These two cell types can be identified in living preparations providing a unique opportunity to analyze the role of SIF cells within autonomic ganglia. The morphological and physiological basis for the effects of acetylcholine, catecholamine, serotonin (5-HT) and substance P on postganglionic neurons will be studied. The following specific questions will be addressed: 1) Identify the chemical nature of the synaptic profiles on postganglionic neurons. In preliminary studies, fibers and cells were found containing serotonin, catecholamines, and a substance P-like peptide in the mudpuppy cardiac ganglion. The synaptology in the ganglion of terminals immunolabeled for these substances will be determined using electron microscopy. 2) Determine the influence of substance P, 5-HT, and catecholamines on the membrane properties of postganglionic neurons and on synaptic transmission between the preganglionic fibers and postganglionic cells. Intracellular recording techniques and voltage-clamp procedures will be used to investigate the action of these transmitter substances on synaptic transmission between the preganglionic and postganglionic cells as well as on the conductance properties of individual postganglionic neurons. 3) Correlate electrophysiological response to applied neuroactive substances with synaptic terminal type and distribution to individual ganglion neurons. Following intracellular recording, neurons will be injected with HRP or lucifer yellow in order to understand the relationship of structure and function in synaptic integration. 4) Determine the effect(s) of SIF cell activity on the properties of adjacent postganglionic neurons. Individual SIF cells will be stimulated intracellularly to determine the influence of SIF cell activation on adjacent parasympathetic neurons and/or on transmission between preganglionic fibers and postganglionic cells. The results of this project should provide significant information about: a) the mechanism(s) of interaction of neurotransmitters on an identified postsynaptic cell, b) the role(s) of SIF cells in autonomic ganglia, and c) the type(s) of integration occurring in vertebrate cardiac ganglia for local reflex control of cadiac function.